(CNN) -- The genocide trial of former Bosnian Serb leader Radovan Karadzic resumed Tuesday at The Hague after a six-week break, with the first witness taking the stand.
Ahmed Zulic testified that he saw Serb forces shelling the mostly Muslim village of Mahala, Bosnia, in May 1992, and that he was one of the few survivors of the Manjaca detention camp.
Karadzic cross-examined the witness later in the session, disputing details of his testimony, both large and small.
Karadzic, who is representing himself, faces 11 counts of genocide, war crimes and crimes against humanity. He has denied the charges.
The charges against Karadzic stem partly from the killing of more than 7,000 Muslim men and boys in the Bosnian town of Srebrenica in 1995. Karadzic, the Bosnian Serb president at the time, is accused of being responsible for the massacre.
It became an emblem for the dissolution of Yugoslavia -- once a multi-ethnic state of Serbs, Croats, Muslims and others -- into six countries during a bloody and brutal conflict in the early 1990s.
Zulic testified that he saw the Serb army and Serbian paramilitaries fire on Mahala in 1992, killing more than 300 civilians in the village near the town of Sanski Most.
"I could see shells flying in and exploding, and of course you could see houses burning at night," Zulic said.
Three women and two brothers were killed in a single house, he said. The only ones left were the infirm or those who had hidden from the shelling because they were unable to leave.
"Those were the ones that were killed when the infantry came to mop up," he testified.
The next month, in June 1992, he was arrested and detained with about 30 others in a small garage where they suffered regular beatings and interrogations, Zulic testified.
The detainees were taken from the garage to a location nearby where "over 20 men were told to dig their own graves." All but three of them were shot or had their throats slit, he said.
In July of that year, he testified, the detainees were severely beaten before being ordered to board a truck to the Manjaca detention camp. Several died along the way because of the extreme heat and lack of air in the truck.
On arrival at Manjaca, the commander refused to accept the dead, and the "extremely dehydrated detainees" had to load the bodies on the truck for the ride back.
Zulic said his weight reduced from 90 to 55 kilograms (198 to 121 pounds) and that he now suffers permanent disability because of the beatings.
Karadzic questioned many details of Zulic's testimony during cross-examination, often making assertions of his own. Both the prosecution and the judges urged the defendant to stick to asking questions.
Judge Howard Morrison closed the session with a word of advice to Karadzic.
Karadzic tended to "engage in comment," the judge said, calling it a "common fault in advocates" of all levels of experience, which Karadzic should "guard against."
Morrison warned that comment "is not a question ... it is not evidence" and that "a comment could be an admission on your part" because Karadzic is both lawyer and defendant.
"If a witness says something and you say that's right ... that could be an admission that you accept the truth of what that witness is saying," Morrison cautioned. "Be very cautious about commenting. It wastes time and it doesn't assist the court."
Karadzic tried but failed to have the trial postponed until mid-June, saying he needed more time to prepare his case.
The trial at the International Criminal Tribunal for the former Yugoslavia (ICTY) began last fall.
Karadzic had refused to appear in court during opening statements, saying he hadn't had enough time for prepare. That led the court to impose a lawyer on him.
The court is now allowing Karadzic to represent himself, with the provision that the standby lawyer will take over if he again refuses to attend court.
The 1992-95 Bosnian conflict was the longest of the wars spawned by the breakup of Yugoslavia in the early 1990s.
Backed by the government of then-Yugoslav President Slobodan Milosevic, Bosnian Serb forces seized control of more than half the country and launched a campaign against the Muslim and Croat populations.
Karadzic was removed from power in 1995, when the Dayton Accord that ended the Bosnian war barred anyone accused of war crimes from holding office.
The trial began more than a year after Karadzic was captured in Belgrade, the capital of Serbia. He had been on the run for more than 13 years and was living in elaborate disguise in Belgrade, practicing alternative medicine at a clinic.
Karadzic would face life in prison if convicted. The court cannot impose the death penalty.
Milosevic died in 2006 while on trial at The Hague.
The ICTY said hearings will be held three days a week at least through the end of April.