LOS ANGELES — Neighbors recall Lance Holger Anderson as a nice, chatty guy who was always ready to help; the kind of person who fixed a flat tire for an elderly neighbor, gave away a Christmas tree to another, and doted on his ailing wife.

So there was shock in his pleasant Canyon Country neighborhood on Wednesday when police arrested Anderson on suspicion of killing his wife, then shooting to death his comatose sister at a Los Angeles nursing home.

The 60-year-old was “the sweetest guy you could ever imagine,” neighbor Grace Madrigal said, holding back tears. The shootings were apparent mercy killings, Los Angeles police Lt. Paul Vernon said.

The family said Anderson’s 63-year-old wife had dementia and his sister, Lisa Nave, 58, had been in the Country Villa Sheraton for five years and was in a “vegetative state” when he allegedly walked into the northern Los Angeles nursing home on Wednesday morning and shot her in the head, Vernon said.

“I want people to understand that this man did not randomly walk into a hospital to commit this crime,” Vernon said.

A resident, David Chabolla, said the gunshot sounded like a balloon popping. He saw Anderson sitting in the nursing home’s courtyard with his head down before police arrested him on suspicion of murder.

A small-caliber handgun was recovered, police said. Anderson remained jailed.

After hearing about the killing, concerned family members contacted authorities and asked them to check on his wife’s welfare. Her body was found Wednesday morning in the couple’s three-bedroom townhome on a leafy, curving street in the Canyon Country area of Santa Clarita, a northern Los Angeles County suburb.

She had been shot with the gun found at the nursing home, a sheriff’s statement said.