Unabomber's Brother 'Heartbroken' Manifesto May Have Inspired Luigi Mangione

Luigi Mangione left a glowing Goodreads review for Ted Kaczynski's 'Unabomber Manifesto' -- and the possibility it inspired Mangione's alleged murder of UnitedHealthcare CEO Brian Thompson is heartbreaking, says the late criminal’s brother.

David Kaczynski tells TMZ he was told yesterday by a friend that Mangione had read the Manifesto ... and it breaks his heart knowing his brother might be seen as a model for acceptable violent behavior.

"It breaks my heart to know in some way – human motivation is very complex -- but in some way, my brother might be seen as a model for acceptable, violent behavior. And in my opinion, there is no such thing" he says.

He explains to us people shouldn’t blur the lines between his brother Ted’s ideas in the Manifesto -- which he believes doesn't necessarily lead to violence -- and his "despicable, hurtful actions," which he says can lead to copycats.

David reminds us acts of violence can be contagious, adding -- if we spread love and kindness, it can do wonders. But if we hurt others, it has the opposite effect -- a very negative one.

There was a Goodreads account under Mangione's name that praised the Unabomber's manifesto as "political revolutionary," giving it a 4-star rating back in January.

Mangione was arrested in Altoona, Pennsylvania on Monday ... and denied bail Tuesday.