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Boston police: Video shows man shot dead had lunged with knife at police officer, FBI agent

  • FBI Special Agent in Charge of Boston Vincent B. Lisi, right to left, Boston Mayor Marty Walsh and Boston Police Commissioner William B. Evans listen to a reporter's question during a joint news conference at the Boston Police Department's Headquarters Tuesday, June 2, 2015, in Boston. A man under surveillance by a joint terrorism task force was shot and killed outside a pharmacy Tuesday after he lunged with a knife at a city police officer when asked to drop his military style knife before the officer and an FBI agent opened fire. (AP Photo/Stephan Savoia)

    FBI Special Agent in Charge of Boston Vincent B. Lisi, right to left, Boston Mayor Marty Walsh and Boston Police Commissioner William B. Evans listen to a reporter's question during a joint news conference at the Boston Police Department's Headquarters Tuesday, June 2, 2015, in Boston. A man under surveillance by a joint terrorism task force was shot and killed outside a pharmacy Tuesday after he lunged with a knife at a city police officer when asked to drop his military style knife before the officer and an FBI agent opened fire. (AP Photo/Stephan Savoia)  (The Associated Press)

  • Boston Police Commissioner William B. Evans answers a reporter's question as Boston Mayor Marty Walsh looks on during a joint news conference at the Boston Police Department's Headquarters Tuesday, June 2, 2015, in Boston. A man under surveillance by a joint terrorism task force was shot and killed outside a pharmacy Tuesday after he lunged with a knife at a city police officer when asked to drop his military style knife before the officer and an FBI agent opened fire. (AP Photo/Stephan Savoia)

    Boston Police Commissioner William B. Evans answers a reporter's question as Boston Mayor Marty Walsh looks on during a joint news conference at the Boston Police Department's Headquarters Tuesday, June 2, 2015, in Boston. A man under surveillance by a joint terrorism task force was shot and killed outside a pharmacy Tuesday after he lunged with a knife at a city police officer when asked to drop his military style knife before the officer and an FBI agent opened fire. (AP Photo/Stephan Savoia)  (The Associated Press)

  • Suffolk County District Attorney Daniel F. Conley speaks as FBI Special Agent in Charge of Boston Vincent B. Lisi, left to right, Boston Mayor Marty Walsh and Boston Police Commissioner William B. Evans, far right, look on during a joint news conference at the Boston Police Department's Headquarters Tuesday, June 2, 2015, in Boston. A man under surveillance by a joint terrorism task force was shot and killed outside a pharmacy Tuesday after he lunged with a knife at a city police officer when asked to drop his military style knife before the officer and an FBI agent opened fire. (AP Photo/Stephan Savoia)

    Suffolk County District Attorney Daniel F. Conley speaks as FBI Special Agent in Charge of Boston Vincent B. Lisi, left to right, Boston Mayor Marty Walsh and Boston Police Commissioner William B. Evans, far right, look on during a joint news conference at the Boston Police Department's Headquarters Tuesday, June 2, 2015, in Boston. A man under surveillance by a joint terrorism task force was shot and killed outside a pharmacy Tuesday after he lunged with a knife at a city police officer when asked to drop his military style knife before the officer and an FBI agent opened fire. (AP Photo/Stephan Savoia)  (The Associated Press)

Police say they have video that shows a man who was under surveillance by terrorism investigators lunged with a knife at a police officer and an FBI agent before he was fatally shot.

Police Commissioner William Evans says members of the Joint Terrorism Task Force approached Usaama Rahim outside a pharmacy Tuesday morning to question him. Evans says Rahim went at the officers with a large military-style knife.

A law enforcement official with knowledge of the investigation said Rahim had been making threats against law enforcement. The official was not authorized to release details and spoke on the condition of anonymity.

Rahim's brother says in a Facebook posting his brother was confronted by three officers while waiting at a bus stop to go to work. He says his brother was shot in the back three times.