Blasts near Baghdad mosque kill 16
Twin suicide bombs also strike Tikrit
Deadly blasts near Shiite mosque in Baghdad.
Arrests in investigation of downing of commercial helo in Iraq.
An insurgent video purports to show a crash survivor's slaying.
Video airing on Al-Jazeera allegedly shows copter being shot down.
BAGHDAD, Iraq (CNN) -- Two explosions rocked western Baghdad's al-Shu'lah neighborhood Sunday near a Shiite mosque and a busy market, killing at least 16 people and wounding at least 57 others, Iraqi police said.
The first bomb went off about 9 p.m. (p.m. ET). When people gathered in the aftermath, a second bomb was detonated about 150 meters from the mosque, police said.
Police originally reported the second bombing as the work of a suicide car bomber who had driven into the crowd, but said later that the device appeared to have been set off by remote control.
Word of the blasts came just hours after news of two suicide car bombs in Tikrit, about 90 miles (150 kilometers) north of Baghdad.
The Tikrit bombs exploded just 15 minutes and a short distance apart, killing at least six people and wounding 26 others at an Iraqi police academy, according to an official with Tikrit's governor's office.
Police were responding to the first explosion -- which happened in front of the police academy at 8 a.m. (12 a.m. ET) -- when the second car bomb detonated close by at the meteorology building, the official said.
The attack in Tikrit, deposed ruler Saddam Hussein's hometown, occurred as new recruits at the academy were about to travel to the Jordanian capital of Amman for a training program, The Associated Press quoted police Lt. Shalan Allawi as saying.
A doctor at Tikrit General Hospital said the bombs killed four policemen and two civilians, with 23 policemen and several civilians wounded, AP reported.
Elsewhere, a roadside bomb killed three insurgents Sunday as they tried to plant it in the town of Mahawil, said police in the nearby city of Hilla.
Arrests linked to chopper downing
The U.S. military has 10 people in custody who are suspected of shooting down a commercial helicopter Thursday, the U.S. military said.
A statement said Task Force Baghdad units, in conjunction with Iraqi security forces, "captured terrorists" believed to have ties to the April 22 attack northwest of Baghdad.
Of the 11 people aboard the helicopter, 10 died in the crash. A survivor, a Bulgarian crew member, was shot dead while on the ground, according to a Bulgarian company that owned the chopper. Six who were killed aboard the chopper were Americans, their employer said.
It was the first known attack on a civilian helicopter in Iraq since the war began.
A statement from Task Force Baghdad said an "Iraqi citizen told the soldiers he knew where the blue Kia pickup truck the terrorists used during the attack was parked and led them to the site.
"When the soldiers got there, several other local residents confirmed the first tip and showed the soldiers where the terrorists lived."
Soldiers searched two houses at 12:30 a.m. The military said troops captured three men and bomb-making materials at one house, and three more men suspected of making bombs at a second home -- but it did not specify where the houses were.
The Americans who were killed in the crash worked for North Carolina-based Blackwater Security Consulting USA. Friday, the company released the names of the employees who died.
They are: Robert Jason Gore, 23, of Nevada, Iowa; Luke Adam Petrik, 24, of Conneaut, Ohio; Jason Obert, 29, of Fountain, Colorado; Steve McGovern, 24, of Lexington, Kentucky; Eric Smith, 31, of Waukesha, Wisconsin; and David Patterson, 27, of Havelock, North Carolina.
Other developmentsA Pakistani Embassy worker reported kidnapped more than two weeks ago has been released unharmed, an embassy official said Sunday. Five days after Malik Mohammad Javaid disappeared after leaving prayers at a Baghdad mosque, his captors released a videotape of him urging the Pakistani government and the international community to intervene and secure his release. Pakistan's Foreign Ministry did not disclose how much the group -- Omer Bin Khatab -- wanted as ransom.A bomb killed a U.S. sailor Saturday who was assigned to the 2nd Marine Division, II Marine Expeditionary Force, the U.S. military said. He was killed while conducting combat operations in Falluja. No other details were released. The report brought the number of U.S. troops killed in the U.S.-led Iraq war to 1,569, according to the U.S. military.Saturday evening, five mortar rounds landed inside a facility in the al-Baiya neighborhood of southwest Baghdad, wounding seven commandos with Iraq's Interior Ministry, Iraq police said. An Associated Press Television News cameraman was killed and an AP photographer was wounded Saturday in the northern city of Mosul, officials said. Saleh Ibrahim and Mohammed Ibrahim -- who were not related, the news agency said -- were shot in a crossfire between U.S. forces and insurgents, said an official at the hospital where Saleh Ibrahim died.A roadside bomb near Abu Ghraib prison killed at least nine Iraqi soldiers Saturday and wounded 20 others, emergency police said. The blast struck an Iraqi army convoy as it passed Zaydan village on the western outskirts of Baghdad.Also Saturday, an Iraqi contractor for the U.S. military was shot to death while driving a truck through Jami'a neighborhood in western Baghdad, Iraqi police said.
CNN's Enes Dulami, Ayman Mohyeldin, Kianne Sadeq and Mohammed Tawfeeq contributed to this report.
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