NASHUA — The police department is investigating criminal allegations against the city’s assessing department.

Those allegations include concerns of potential mileage fraud and unexplained reductions to property assessments, according to Nashua Police Chief Mike Carignan.

“We are in the middle of that investigation right now,” said Carignan, adding the investigation was launched about two months ago.

Carignan said Nashua resident Laurie Ortolano, who hired a private investigator to follow a city assessor while he was on the job, approached police with her concerns.

Carignan then spoke with Mayor Jim Donchess about the allegations, at which time Donchess requested that an investigation be opened. The chief said the mayor does not believe that any criminal activity has occurred.

Donchess, Ortolano and Kim Kleiner, director of administrative services for the city, have all been cooperative throughout the investigation, said Carignan.

“There is a lot of information. There is an inundation of information,” he said, acknowledging that there is also a learning curve as investigators study the revaluation of properties.

According to Ortolano, there was a combined $24 million reduction in assessments of 13 properties made on Oct. 10, 2018 — after homeowners and business owners were already notified of their new property valuations and just days prior to the final capture deadline for property cards in anticipation of the upcoming tax bills.

“Those are big changes,” said Ortolano, who first brought her concerns to the city last year.

She said one unidentified property’s assessment was reduced by $4.4 million.

Another, 138 Spit Brook Road, home to World Academy, received a $2.4 million cut in its assessed value.

“There is no audit trail for any of these changes,” said Ortolano, explaining if other residents were not pleased with their assessments, they had to file an abatement request to get a reduction.

Kleiner told city officials earlier that the $24 million reduction in assessed value was related to a code change for schools and institutional properties, which needed to be adjusted.

“Although $24 million sounds like a lot, the greatest share of that is nontaxable money anyway,” attorney Steve Bolton, corporation counsel for the city, said on Thursday.

This week, Kleiner told aldermen that there was a lack of mileage reporting discovered during a previous management audit of the assessing department. Now, all assessors are required to submit mileage field logs, which are reviewed and approved by the director and verified against schedules from administrative staff, when applicable.

In addition, Kleiner said she is now informed of all assessment changes over $20,000.

Bolton said he has faith in the police department, noting that anyone can make a complaint to police and allege some type of illegality and they will investigate.

If irregularities occurred, he said, the city wants to correct that and take appropriate action.