Guatemala City, Guatemala (CNN) -- Two fugitive brothers wanted in the much-publicized slaying of a Guatemalan lawyer last year were being held at a military base Tuesday, one day after they surrendered to authorities with a special United Nations commission, the Guatemalan Defense Ministry said.
Businessmen Francisco Jose Ramon Valdes Paiz and Jose Estuardo Valdes Paiz had been sought since December on charges that they masterminded the assassination of lawyer Rodrigo Rosenberg. The lawyer left behind a videotape saying that President Alvaro Colom would be responsible if anything happened to him.
The International Commission Against Impunity in Guatemala, known by its Spanish acronym CICIG, determined that Rosenberg orchestrated his own death in order to implicate Colom, whom he blamed for the recent slayings of two close friends.
The Valdes Paiz brothers were unaware that Rosenberg duped them into carrying out his own slaying, CICIG said in January, when the commission released the results of an eight-month investigation. Rosenberg had told them told them he was being threatened by someone and wanted that person killed, the CICIG investigation concluded.
Colom had nothing to do with the killing, CICIG said.
The brothers' surrender came suddenly Monday morning when their lawyer called CICIG headquarters at 8 a.m. and said they wanted to turn themselves in, said Carlos Castresana, head of the U.N. agency. The brothers were in custody less than a half hour later, Castresana said at a news conference.
The men chose to turn themselves in to CICIG out of concern for their personal safety, said Castresana, a Spanish judge.
They were handed over to Guatemalan authorities.
The brothers are being held at the Matamoros military base, said defense ministry spokesman Col. Byron Gutierrez.
Rosenberg was shot from behind in May 2009 in a brazen daylight attack while riding his bicycle in Guatemala City, the nation's capital. He was shot three times in the head, once in the neck and once in the back, Castresana said in January when he presented the results of the investigation.
The two brothers, who own a pharmaceutical company, had been cousins of Rosenberg through a previous marriage and did not know that he was the target of the assassination, Castresana said.
Rosenberg fed information to the hit squad leader that led to his own death, giving descriptions of what the target looked like and where he would be.
"It was the two brothers and no one else," Castresana said. "Not a politician. Not a [government] minister. Not a police chief. No one. Just these two brothers."
About 300 investigators from 11 nations reached their conclusion after an exhaustive examination of 100,000 telephone calls, 9,500 documents, surveillance videotapes and 135 interviews with 11 suspects and others, Castresana said.
Colom had maintained since the May 10 slaying that he was innocent despite Rosenberg's explosive videotape, which was made public the day after his death.
Before Monday's surrender by the brothers, Guatemalan authorities had already arrested 11 men on suspicion that they carried out the killing.
Arrest warrants for the brothers were issued December 10, Castresana said.
Rosenberg recorded the tape blaming Colom three days before his death.
He said Colom wanted him dead because the lawyer had been blaming the president and some of his top associates for the slaying of prominent businessman Khalid Musa and his daughter, Marjorie, the previous month.
They were killed, Rosenberg said, because they had refused to participate in acts of corruption as the president wanted.
Rosenberg was Musa's attorney.
Castresana indicated Rosenberg staged his own killing to get back at Colom and high-level members of his government, whom he could not prove were responsible for the Musa killings.
"He wanted to open a box of lightning and thunder," Castresana said.
Castresana pointed to several indicators of Rosenberg's state of mind: His mother had died; he was going through a second divorce, and his wife had taken their young children to Mexico; he was bereft at the slaying of Marjorie Musa, with whom he had a close relationship; and he felt a sense of powerlessness because he could not prosecute the people he believed were responsible for the Musa slayings.
May 10, the date of his killing, was Mother's Day.
In two April 21 e-mails, seven days after the Musa killings, Rosenberg wrote, "I can't stop crying" and "I feel like I'm disintegrating," Castresana said.
Rosenberg made out his last will and testament on April 24 and started going public with his accusations against Colom regarding the Musa slayings on May 3.
On May 4, he called a meeting at his law office and said he would be leaving the firm, in which he was a partner.
The next day, Castresana said, Rosenberg asked a friend to buy two cell phones anonymously. Those cell phones, the lead investigator said, were crucial to cracking the case.
Rosenberg used one of the phones to call threats to his personal cell phone and had the other delivered to the Valdes Paiz brothers, who gave it to the hit squad leader. Rosenberg then used the new cell phone he kept to give instructions to the hit squad leader through the second phone, Castresana said.
Castresana detailed how the slaying apparently was meant to be paid through a check of about $40,000.
According to the investigator, Rosenberg told his secretary before his death that she would be receiving a check from Panama that should be delivered to the Valdes Paiz brothers. The check had been made out by Luis Alejos, a Rosenberg friend and business associate who at the time was Guatemala's minister of communication, Castresana said. Alejos resigned from office in June, a few weeks after the slaying.
After receiving the check, Francisco Jose Valdes Paiz destroyed it, Castresana said. The businessman paid the 300,000 quetzales ($35,900) for the assassination out of his own pocket, Castresana said.
Alejos is the brother of Roberto Alejos, the president of the Guatemalan Congress, and a cousin of Gustavo Alejos, who was President Colom's private secretary at the time.
In his videotape, Rosenberg said Gustavo Alejos would be among those responsible for the lawyer's death if it happened.
"If you are reading this message, it means that I, Rodrigo Rosenberg Marzano, was murdered by the president's private secretary, Gustavo Alejos, and his associate Gregorio Valdez, with the approval of Mr. Alvaro Colom and [first lady] Sandra de Colom," Rosenberg said.
After the tape surfaced, Colom went on national TV with a strong denial that he or anyone mentioned in the video was involved.
He expressed his sense of vindication in a televised speech in January.
"I don't have any rancor in my heart," Colom said. "Just immense gratitude for those who waited patiently with us."
The United Nations established the International Commission Against Impunity in Guatemala in 2006 to investigate corruption and political violence. More than 200,000 people have been killed in the nation since 1970, mostly as a result of organized crime, drug-trade violence and a 36-year civil war that ended in 1996.
There were 6,451 slayings in Guatemala in 2009, in which only 230 verdicts were achieved, Castresana said. That means, he said, that more than 96 percent of the killings last year were not solved.
Journalist Alexia Rios Hayashi contributed to this report for CNN.