Gannon's K-9 partner, Nero, was wounded.
The dog is under "full 24/7 law enforcement protection" and will remain in the care and control of the Yarmouth Police Department's K-9 Unit and K-9 units across New England, according to the Police Department.
At the time he was shot, Gannon was serving a warrant with his dog, Nero, and other officers from Yarmouth, Barnstable and the state police. He was held without bail in Barnstable District Court on Friday.
Not-guilty pleas to charges including murder were entered on his behalf, and the judge said she would appoint a lawyer to represent him.
Massachusetts Gov. Charlie Baker has ordered flags across the state flown at half-staff after a police officer was shot dead Thursday on Cape Cod while serving a warrant.
"We're going to miss him terribly, our department is going to miss him terribly", said Police Chief Frank Frederickson. Baker also ordered all US and state flags on state buildings lowered to half-staff in honor of the fallen officer. He previously worked for the Nantucket and Stonehill College police departments.
Cape and Islands District Attorney Michael O'Keefe said Latanowich had just served four to five years in state prison for gun charges.
Latanowich, who previously lived in West Yarmouth, had well over 100 criminal charges in MA before Thursday's arrest.
Gannon, who was the Yarmouth Police Department's first full-time drug detection K-9 patrol officer, leaves behind a wife, Dara.
Latanowich entered the court with his head down.
A tragedy. Our hearts are with Yarmouth Police Officer Sean Gannon killed today in the line of duty, and with his family and fellow officers.
Latanowich, a career criminal with 111 prior charges on his record, was arrested after an hours-long standoff with police.