The police in Sacramento, searching for someone reported to have been breaking windows, fatally shot a young black man in his backyard over the weekend after he walked toward them carrying what they believed was a gun.

When they examined his body, however, the only object they found was a cellphone.

That was the account that the Sacramento Police Department offered on Tuesday in an update to their investigation into the shooting by officers of the unarmed man, 22-year-old Stephon Clark, on Sunday.

Mr. Clark’s relatives, whom he lived with in the South Sacramento neighborhood, could not immediately be reached on Wednesday. But one of them told The Sacramento Bee that family members often entered the home through the garage, after knocking on the back window because the doorbell was broken.

“The only thing that I heard was pow, pow, pow, pow, and I got to the ground,” said Sequita Thompson, Mr. Clark’s grandmother, adding, “I opened that curtain and he was dead.”