An armed robber opened fire on residents of a Casselberry home that he broke into when they chased him down the street early Monday morning, according to police.

Casselberry police said the masked man walked into the unlocked duplex on Lake View Drive, snatched a purse and then fled.

"It was very fast. He was in and out. He grabbed the lady's purse and she ran out after him, kind of surprised and he turned around and fired a shot at her," said Sgt. William Nas of the Casselberry Police Department.

Police said they found a number of bullet casings in the street, but there was no sign of the man.

"Is that the kind of thing that happens around here?" WFTV reporter Steve Barrett asked.

"Not as a rule, but there's a lot of questionable stuff that goes on around here," said neighbor Bruce Whiting.

Investigators said officers were searching for the man, but have a vague description of him.

"He was wearing a mask, so obviously some pre-planning there. He opened the front door, so the door wasn't secured. That was how he got in," said Nas.

Police said the victims made another mistake: They called a friend to tell them about the crime first, delaying the call they made to police to report the intruder.