A recent Harvard alum said he chased an intruder out of Mather House yesterday afternoon and trailed the suspect for two blocks until police arrived at the scene.

Joseph K. “J.K.” Costello IV ’03-’04 said he stepped off the elevator on the 14th floor of Mather Tower around 2:30 p.m. yesterday and saw a man wearing a silver coat and stocking cap walk out of Costello’s suite.

“I knew immediately that he didn’t have any business being there,” said Costello, who has worked in Mather as an assistant—or “elf”—to the House administration since graduating from the College in January.

“I know all the people who live near us,” he said. “[The suspect] looked at me, I looked at him, and he took off running.”

As the suspect headed for the staircase, Costello said he returned to his suite, but didn’t immediately notice anything missing. He left his room and knocked on nearby doors, “but no one was around,” he said.

Costello said he then rode the elevator down to the first floor, calling the Harvard University Police Department (HUPD) from his cell phone en route. When he arrived on the first floor, he again saw the suspect exiting Mather Tower.

“I saw him walking around the courtyard and I started to follow him,” Costello said. “I judged that he wasn’t really a threat. He didn’t make any moves towards me...He didn’t seem like he wanted any piece.”

Costello described the suspect as a 5’9 black male and estimated the suspect’s age at 40-50 years.

“He was old so he realized he couldn’t run away from me,” Costello said.

Costello said he walked 10 to 20 feet behind the suspect, meanwhile staying on his cell phone with a HUPD dispatcher.

The suspect “threw something out of his pocket on Bank Street,” Costello said. “It was a credit card, and I picked it up.”

Moments later, Costello said, he watched four HUPD officers—one on bicycle, one on foot and two in a patrol car—surround the suspect and make an arrest.

Costello said less than two minutes elapsed from the time he called HUPD on his cell phone to the time the police arrived near the intersection of Bank Street and Mt. Auburn Street.

HUPD’s response time was “pretty impressive,” Costello said.

The credit card, a VISA, belonged to Siddharth B. Shenai ’04, a physics concentrator who lives on the 17th floor of Mather Tower.