The estate of a Boston man who was shot to death by a city police detective and an FBI agent in 2015 during a terrorism investigation is suing the federal government for $5 million on wrongful death allegations.

Usaamah Rahim and two other men were accused of participating in a plot to behead conservative blogger Pamela Geller, who angered Muslims by organizing a Prophet Muhammad cartoon contest in Garland, Texas, in 2015. The plot was not carried out.

Authorities said officers shot the 26-year-old Rahim when he lunged at them with a knife in Boston. At the time, an anti-terrorism task force was surveilling Rahim around the clock because authorities had learned of the beheading plot.

Suffolk District Attorney Daniel Conley concluded the officers were justified in shooting Rahim.

The Boston Globe reported Rahim's estate filed the lawsuit in federal court in Boston on Thursday. It alleges law enforcement officers "unlawfully seized, assaulted and killed" Rahim, and accuses officials of acting "negligently and recklessly in their use of excessive force, and deadly force."

The lawsuit also says no fingerprints were recovered from the knife and there were inconsistent accounts by officials about how Rahim pulled the knife.

The FBI and Boston police declined to comment.

Authorities said Rahim's nephew, David Daoud Wright, and Nicholas Rovinski also were in on the plot against Geller. Wright is serving a 28-year prison sentence for conspiring to kill Americans on behalf of the Islamic State, and Rovinski is serving 15 years behind bars for plotting to commit acts of terrorism.

During the 2015 cartoon contest, two other men opened fire outside and wounded a security guard before they were killed in a shootout with law enforcement assigned to guard the event.

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Information from: The Boston Globe, http://www.bostonglobe.com