WESTFIELD -- A mysterious stalker known only as "The Watcher" has sent a fourth threatening letter to a township home that arrived in February, less than three weeks after a renter moved into the infamous home.

Derek and Maria Broaddus, the owners of the six-bedroom house on Boulevard, bought the property for $1.3 million in June 2014 and within days received the first letter from somebody identifying himself as "The Watcher."

Two more letters arrived in the following weeks, all containing threats, two of them asking if the owners had "young blood," a reference to children. The owners, who have children, refused to move into the home.

Lee Levitt, the Broaddus' attorney in their suit against the prior owners of the home, filed a legal brief early this month in which he revealed a fourth letter had arrived. Levitt, in the court papers, said a tenant moved in Feb. 1, and the latest later came days later.

"On or about Feb. 20, 2017, Plaintiffs received a fourth letter from 'The Watcher'," Levitt wrote in the brief.

"This letter contained specific threats and was more derogatory and sinister than any of the previous letters," the brief states.

The latest missive is under investigation by police, the Union County Prosecutor's Office and the U.S. Postal Service.

The prosecutor's office declined to comment when asked about the letter. The postal service referred all questions to Westfield police.

When asked recently about any threatening letters coming to the house, Westfield police said there was a continuing investigation and did not comment further.

In June 2015, a year after buying the house, the Broadduses filed suit against the prior owners, John and Andrea Woods. The Broadduses say they can not move into the house, and the letters scared off any prospective buyers.

The couple said the Woods had received a letter from the stalker days before the closing, but never disclosed it.

That lawsuit, which included parts of the three letters, gained worldwide attention. As a result, the Woods counter sued, saying they had been defamed. They admitted receiving a letter, but said it was not threatening.

Levitt did not include the latest letter in the court papers because of the state and federal investigation.

When reached Tuesday, Levitt declined to comment on the latest missive.

On Feb. 7, a man answered the door at the house and said he started renting it Feb. 1. The man, who would only give his name as Chris, indicated he had no concerns about the threats in the first three letters, saying they were "not my issue."

No one answered the door at the house late Tuesday.

Last year, the Broadduses tried another route for ridding themselves of the home. The couple applied to the township for a permit to subdivide the property in a plan to demolish the house and replace it with two new ones. In January, the planning board, after hearing objections from neighborhood residents who said the smaller lots would be out of character, rejected the application.

Earlier this month, the Broadduses filed suit in court seeking an order overturning the board's decision.

Tom Haydon may be reached at thaydon@njadvancemedia.com. Follow him on Twitter @Tom_HaydonSL. Find NJ.com on Facebook.