GRAND RAPIDS – The author of a letter threatening violence against East Hills residents, already on edge from a recent arson that destroyed an under-construction townhouse, has become calculated and deliberate in his efforts to strike fear in people, a retired state police lieutenant and psychologist says.

The person, or people, also are likely to be searching for relevance in a move likely unprecedented locally, according to authorities.

“What struck me is that somebody's trying to belong to a crowd,” said John Hulsing, the former state police commander. “The question is what is the crowd and why.”

Signed by "The Old Neighbors," a menacing letter delivered to residents Friday warns people in the "suburbanite cul-de-sac," that a Feb. 22 arson was carried out by a group of anti-gentrification militants. There are no cul-de-sacs in that area of East Hills.

The group claims to have placed three incendiary devices in a townhouse at 914 Blodgett St. SE. The residences are part of a revitalization effort in the Southeast Side area that has seen a marked increase in new housing and improvements to century-old structures. There has also been an influx of retailers and restaurants.

The threats pull no punches, previewing possible muggings, burglary and kidnappings if occupants are forced back into the suburbs and the area restored to low-income housing.

“This attack was not isolated, nor will it be the last,” it states. “We are not peaceful. We are not willing to negotiate. You, your families and material possessions are at stake.”

Grand Rapids police Capt. Jeff Hertel said his investigators have teamed with the local FBI terrorism unit and the Bureau of Alcohol, Tobacco and Firearms. Federal authorities declined to comment on their role, deferring to Grand Rapids officials.

“We are taking this very seriously,” said Hertel. “Spray painting is one thing, but when you're threatening someone, that's another (level).”

Hertel referred to earlier crimes that targeted and defaced businesses, including The Electric Cheetah and Brick Road Pizza Co. and The Winchester bar. Police can't say definitively if the same people responsible for that vandalism, spray-painting and throwing bricks through windows and doors, are behind the arson and letter.

As for the letter, Hertel said: “I've never heard of it happening here. It's certainly a rare occurrence.”

Authorities are hesitant to put a limit on the investigation or possible suspects, saying the potential reasons behind the attack are wide-open. It could be linked to the anti-gentrification cited, a political message or a cover-up for something else.

Making the jump to violence perpetrated by the Earth Liberation Front, which set fires to stymie development and their perception of environmental destruction, or to a Unabomber-like Ted Kaczynski is premature.

Hulsing, who has extensively interviewed prison inmates about the motivation for their offenses, says the recent incidents don't strike him as a move from an impulsive criminal.

“This seems to be more calculating,” he said. “They believe the thoughts are rational.”

Hulsing is hopeful for one link to Kaczynski. He was turned in by his brother, who recognized the language in his manifestos.

“Somebody, an educator, a friend or a family member, might be able to pick this out and protect people,” Hulsing said.

Police have increased patrols in the East Hills area but are not disclosing other strategies to apprehend suspects.

Neighbors, who were to meet Monday, said they fear the threats, but have no inclination to move from the area in the two-month time frame demanded in the letter.

“This is all kind of crazy and the motivation, whatever it is, makes no sense,” said one resident, who declined to be identified. “This area is up-and-coming and why would you want to destroy that?”

Many homes, once neglected or owned by largely-absent landlords, are being purchased, renovated and used as single-family residences.City commissioners voted in 1999 to make the areaa historic district.

Since then, the first new housing development in 50 years has begun and the former D.A.BlodgettChildren's Home has been renovated to the home of the Inner City Christian Federation, a non-profit aimed at providing safe and affordable housing.

E-mail Nate Reens: nreens@grpress.com and follow him on Twitter at twitter.com/natereens