He was in a group of fellow officers from Yarmouth, Bourne and state police serving a warrant in Marstons Mills.
Massachusetts Gov. Charlie Baker tweeted that he was "heartbroken" after hearing about the officer's death and said his thoughts and prayers were with Gannon's "family, loved ones and the @yarmouthpolice after this tragic loss".
A MA police officer was reportedly shot and killed Thursday while serving a search warrant to a man with an extensive criminal history.
"We're going to miss him terribly, our department is going to miss him terribly", said Police Chief Frank Frederickson.
Latanowich entered the court with his head down.
"We will together get through this, and we plan to keep Sean's memory alive", said Frederickson".
On Thursday, police went to a home in Barnstable to serve an arrest warrant on Latanowich for a parole violation. "He had a probationary sentence after that".More news: Pres. Trump pardons Scooter Libby
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An eight-year veteran of the force, Gannon was married and a graduate of both Bishop Stang High School in Dartmouth and Westfield State University.
Gannon's dog, Nero, was also shot. Dennis Veterinary Hospital posted on Facebook that Nero was shot in the face and neck but has been stabilized and faces surgery today (Friday).
Yarmouth's state Rep. Tim Whelan, previously a state police sergeant, and had worked at the Yarmouth barracks, knew Gannon personally.
Gannon was 32 and had been with the Yarmouth police for 8 years.
Tom Latanowich, 29, has had more than 110 prior criminal charges.
The Okay-9 officer died after he was shot throughout the head, a police provide knowledgeable Fox 25 Boston. He was serving the warrant in the town of Barnstable.