A set of 25-30 paintings, collectively valued at at least $27 million, was stolen from a recently retired Harvard oncologist and his business partner on Friday at their rented home in Pebble Beach, Calif.

The owners of the artwork, retired Harvard doctor Ralph Kennaugh and Angelo B. Amadio, reported that the stolen art included works by Matisse, Miro, Rembrandt, and Renoir. The most valuable piece was a Jackson Pollock painting estimated to be worth $20 million.The paintings were part of a collection of over 100 pieces of artwork.

According to Amadio, the stolen art was stacked in the hallway of their home. The two owners had been planning to move out because a security company had refused to install a security system, he said.

A 2002 insurance appraisal valued the collection at $27 million. But according to Amadio, a more recent assessment put the worth of the combined collection at upwards of $80 million.

Commander Mike Richards of the Monterey County Sheriff’s Office said the police have several suspects but added that he could not divulge further details while the investigation is ongoing.

Amadio said that he believes the theft to be an inside job because the thieves were able to differentiate between the authentic pieces and reproductions.

He said that only six people knew of the collection in the house.

Kennaugh told the Boston Globe that he has been collecting art for the past 30 years without having a work of art stolen. Richards also noted the unusual nature of the case. “We have not had cases of this nature in recent years,” he said.

Amadio and Kennaugh are offering a $5 million reward for the return of the artwork in its original state and for evidence leading to the arrest of the perpetrators.

According to Amadio, a ransom note was found that demanded money and also included a death threat. “If someone tries to kill you for [the artwork], you let it go,” he said.