(CNN) -- A lawyer who left a videotape saying Guatemalan President Alvaro Colom would be responsible if anything happened to him masterminded his own death last year, a special United Nations commission said Tuesday after an eight-month investigation.





Colom had nothing to do with the killing, said Carlos Castresana, head of the International Commission Against Impunity in Guatemala.





"Rodrigo Rosenberg, for some reason, decided to put an end to his life," Castresana said at a televised news conference.





Rosenberg was shot from behind 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.





Prominent Guatemalan brothers Francisco Jose Valdez Paiz and Jose Estuardo Valdez Paiz hired hit men at the behest of Rosenberg, who told them he was being threatened by someone, Castresana said.





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.





Guatemalan authorities have arrested 11 men on suspicion that they carried out the killing, but the Valdez Paiz brothers remain at large.





Their lawyer, Alexis Calderon, denied last week that his clients were involved.





"This is a story being made up to implicate people who didn't have anything to do with it," Calderon said.





He also said that he did not know where the brothers were but that they would surrender after Tuesday's conference.





Calderon did not answer calls seeking comment Tuesday.





Arrest warrants for the brothers were issued December 10, Castresana said, noting that the suspects were already out of the country by then.





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 a prominent businessman and his daughter the previous month.





Businessman Khalid Musa and his daughter, Marjorie, 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," said Castresana, a Spanish judge.





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
UN   commission included how many investigators? What did the lawyer leave? what did the tape say? how many investigators? How many investigators were there? UN   commission is from how many nations? Who felt vindicated?
300 a videotape Guatemalan President Alvaro Colom would be responsible 300 About 300 11 Guatemalan President Alvaro Colom
question: UN   commission included how many investigators?, answer: 300 | question: What did the lawyer leave?, answer: a videotape | question: what did the tape say?, answer: Guatemalan President Alvaro Colom would be responsible | question: how many investigators?, answer: 300 | question: How many investigators were there?, answer: About 300 | question: UN   commission is from how many nations?, answer: 11 | question: Who felt vindicated?, answer: Guatemalan President Alvaro Colom