Suffolk police arson detectives explained to jurors Tuesday how they determined that a series of fires in vacant Central Islip houses were intentionally set in late 2017.

Prosecutors say those fires were set by the two men on trial, firefighters Stephen Hernandez, 25, of Central Islip, and Weldon Drayton Jr., 35, of Brentwood. Prosecutors accuse the defendants of setting the fires so they could build fire house credibility by responding quickly. But defense attorneys continued to critique a probe in which investigators seemed to gloss over evidence and, in one instance, threw it away without documenting it.

Retired Det. Paul Waldvogel  testified that he responded on Oct. 21, 2017, to the aftermath of a fire on Gates Avenue and determined that two fires were set there. There was one spot where fire damage showed it began outside, beneath a window, he said during questioning by Assistant District Attorney Luigi Belcastro. And in the living room, Waldvogel said irregular burn patterns in the carpet showed that fire began there as well.

During cross-examination, Hernandez's attorney, Caroline Mayrhofer of Hauppauge, focused on evidence that Waldvogel either paid little attention to or, in one case, collected and then threw out after he decided it had no value to the investigation.

He testified he noted a bunch of metal discs in the living room near the burn patterns. He said he thought if they were the remnants of tea light candles they might have had something to do with the fire, so he put them in a paper bag and took them back to police headquarters in Yaphank. But when he looked at them more closely there, he said, he realized they weren't tea light candles and threw them away.

"How often do you take evidence from a scene and throw it away?" Mayrhofer asked.

"Never," Waldvogel replied, other than this time.

Later, during further questioning by Belcastro, he said the discs had nothing to do with the fire.

"It was by no means a candle," he said. "I should have examined them closer at the scene. I did not."

Mayrhofer suggested there were other things he didn't examine closely at the scene. They included an undamaged travel mug found in the middle of one of the scorch marks on the living room carpet. Another item was a ladder against an outside wall near a living room window. Waldvogel said he took no pictures of it and did not examine it.

He said he later learned that probationary firefighter Austin Lehman, 20, of Central Islip, said he used a ladder to get into this house to set the arson. Lehman, who will testify later in the trial under a cooperation agreement, has pleaded guilty to setting all the fires in the case.

Waldvogel conceded that if he'd examined the ladder, he might have been able to collect DNA evidence, clothing fibers or shoe prints on the ladder.

Another witness, Emily Flores, a next-door neighbor to a Gibbs Road house that was set on fire on Nov. 7, 2017, narrated a video from her home surveillance system that showed two people walking toward and away from that house several hours before it was noticed burning. The people are not identifiable on the video.

During questioning by Mayrhofer's co-counsel, Steve Politi of Central Islip, Flores said she knew Lehman, a friend of her younger brother. He stopped by not long after the fire.

"I asked him if he knew anything about it," she said. He said then that he didn't, Flores testified.

Det. Dominic Arpino testified about an Oct. 24, 2017, arson fire on Vanderbilt Avenue. He said he asked a next-door neighbor about his surveillance cameras.

"He just walked away," Arpino said, explaining why he never saw the video. "I didn't press the issue any further."

Arpino will be cross-examined Wednesday.

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