LOWELL -- On a November morning in 2017, Lowell police detectives made what appeared to be a typical drug arrest.
They spotted a man they knew used drugs and watched as he allegedly purchased heroin from a green Honda Civic on Ames Street.
Within moments, police stopped him and approached the car, where they encountered Hector A. Gomez, 36, a Lowell resident with a history of arrests for alleged drug offenses, records show.
The detectives arrested Gomez and seized $632, a bag of suspected heroin, and two cellphones from the car, a police report said.
But when Gomez’s case was called for trial in Lowell District Court on Nov. 28, the charges were dismissed because some Lowell police officers are prohibited from testifying, pending an internal review of their role in the arrest of Paul Aaron, 31, a suspected fentanyl dealer.
Gomez’s case is among 15 that have been dropped since early November because the officers can’t testify. Aaron was arrested in Lowell on March 7.
The Globe reviewed the 15 cases on Wednesday based on information from the Middlesex district attorney’s office. Twelve involve drug offenses, three deal with firearms or ammunition charges, and one alleged an illegal sports betting and lottery operation.
Two defense attorneys whose clients had their cases dismissed have also asked prosecutors for information it may have concerning a possible investigation into the Lowell detectives by the US attorney’s office in New Hampshire.
In separate letters written last month, Steven J. Rappaport and Roland M. Milliard said the federal prosecutor’s office in New Hampshire may be investigating some members of the Special Investigations Section.
Lowell police Captain James Hodgdon said Wednesday that he is not aware of any investigation beyond the internal review into three detectives placed on paid leave on Nov. 2.
Attorney Douglas I. Louison, who represents the three detectives , plus a fourth detective who was also involved in Aaron’s arrest, said federal authorities haven’t interviewed his clients.
Federal prosecutors in New Hampshire said Wednesday they couldn’t confirm or deny such an investigation.
The internal police investigation is focused on whether the officers made false statements in reports and an affidavit filed in the case of Aaron, who was arrested wearing a bullet-proof vest and carrying a bag containing a suspected kilo of fentanyl.
Louison identified the detectives as Nicholas Dokos, Rafael Rivera, and David Lavoie. He said he also represents, Detective David Kew, who participated in Aaron’s arrest, but wasn’t placed on leave.
Hodgdon said initially all Lowell police officers present at Aaron’s arrest were prohibited from testifying in court, but the department later narrowed its order to the three officers on leave.
Meghan Kelly, a spokeswoman for Middlesex District Attorney Marian T. Ryan, said the affected cases were in Lowell District Court and dismissed without prejudice, meaning they could be prosecuted later.
Louison said the dismissals are “premature.”
“These detectives have not engaged in misconduct. They have done their job by taking kilos of fentanyl off the street,” he said.
Additional cases may also be jeopardized. In a letter filed in court, Rappaport identified two pending drug cases that may be impacted. One client is charged with distributing heroin and the other is accused of trafficking cocaine.
Two of Rappaport’s clients have already seen their cases dropped because Lowell detectives couldn’t testify.
One case involved Derek Lemire, 40, of Dracut, who was accused of distributing prescription drugs and had more than $87,000 in his house when he was arrested in June, court papers show.
Lemire’s case was dismissed Nov. 2.
Rappaport also represented Kevin V. Ros, 32, a Lowell resident, who was arrested on May 24 after police found what they believed to be a pound of marijuana in his car, a police report said.
On Nov. 16, a judge allowed Rappaport’s request to keep the suspected marijuana and $1,396 taken from Ros out of the case because Lowell officers didn’t attend a hearing where prosecutors planned to contest the petition, court records show.
The case was dismissed on Nov. 30. Hodgdon said he was reviewing the matter, noting the officer who arrested Ros had no role in Aaron’s case.
Lowell police assisted in the operation that led to Aaron’s arrest at the request of New Hampshire State Police Trooper Francisco Vicente, who was working on a larger investigation involving 45 people suspected of trafficking fentanyl.
State prosecutors charged Aaron, but stopped the prosecution in October after “potential inconsistencies in the evidence” emerged.
He remains in custody on federal drug charges in New Hampshire related to the alleged fentanyl operation and has pleaded not guilty.
Inconsistencies in the police account of Aaron’s arrest emerged on Oct. 9 when the defense asked for some evidence to be thrown out during a hearing in federal court in Concord, N.H. Vicente testified.
A key issue was the shopping bag allegedly containing suspected fentanyl that Aaron was holding when he was arrested in Lowell.
Vicente testified that he watched Aaron approach a livery car, lean in the window, and then walk away carrying the shopping bag, according to a transcript of the hearing.
He said Aaron wasn’t carrying the bag before approaching the vehicle — a crucial detail, the defense wrote in court papers, because officers said it provided probable cause to stop Aaron.
But surveillance video from the scene of the arrest shows Aaron was carrying a bag before he approached what police described as the vehicle and after he walked away.
Vicente’s testimony was similar to a police report and an affidavit about the arrest prepared by Lowell detectives, Aaron’s lawyer, David H. Bownes wrote in court papers.
After the video was played during the hearing, Bownes’s request to toss some evidence against Aaron was approved.
A New Hampshire State Police spokesman declined to comment Wednesday about Vicente.