Here is a excerpt from an article by Marlow Stern of the Daily Beast:  
http://www.thedailybeast.com/articles/2016/01/10/making-a-murderer-meet-the-men-steven-avery-thinks-may-have-killed-teresa-halbach.html
 
At the time of Halbach’s murder, the mustachioed Tadych was dating Barb Janda, the sister of Steven Avery who lived next door to him (they’re now married). Janda is the mother of Bobby, Blaine, Bryan, and Brendan Dassey. In the series, Tadych delivers a strange statement to the press the day after Avery’s conviction, saying, “What happened yesterday is the best thing in the world,” adding, “He got what he got comin’ to him.”
 
According to Avery’s court filing, Tadych’s “previous experiences with the court system show him to be a violent and impulsive person, particularly towards women.” In 1994, Manitowoc County charged him with criminal trespass and battery, with the complaint alleging that Tadych visited the home of Constance Welnetz at 3 a.m., knocking on her bedroom window. Welnetz was asleep with a man named Martin LeClair, and as she called the police, Tadych is alleged to have walked into her home and told her, “You will die for this, bitch.” Then, LeClair went outside to confront Tadych and Tadych struck him, knocking him briefly unconscious.
 
It didn’t end there. In 2001, Welnetz filed a temporary restraining order against Tadych, alleging he’d call her “repeatedly at work within short periods of time,” threatened to “kick her ass,” followed her, and once pushed his way into her home. Then, in 2002, Tadych was arrested for assaulting Welnetz. After she allegedly tried to kick him out of her home for yelling at her son, Tadych “shoved Welnetz against the wall, took her phone and threw it on the floor so she could not call the police,” and “twice punched Welnetz in the shoulder with a closed fist,” according to Avery’s court filing.
 
As far as Teresa Halbach goes, Avery claims Tadych was at the Janda home on the Avery Salvage Yard property twice on Oct. 31, 2005, the day Halbach was murdered. And it was Barb Janda’s van that Halbach had come to photograph, so “Barb, and likely Tadych, knew Ms. Halbach would be coming to the yard to photograph the van.” What’s more, Tadych’s only alibi is Bobby Dassey, who is now Tadych’s stepson. In fact, they’re mutual alibis in the case, claiming each saw the other while driving on their way to hunt, and that, according to the Avery filing, “no one else can vouch for their whereabouts during that afternoon.”
 
And according to Avery’s court filing, which cited a Calumet County Sheriff’s Department report, a co-worker of Tadych’s “reported that Tadych had approached him to sell him a .22 rifle that belonged to one of the Dassey boys,” and a .22 rifle is believed to be the weapon that killed Halbach. Also, a co-worker stated to the Calumet County Sheriff’s Department that Tadych “had left work on the day that Steven Avery was arrested, and that he was a ‘nervous wreck’ when he left.” Yet another co-worker allegedly overheard Tadych saying that “one of the Dassey boys had blood on his clothes, and that the clothes ‘had gotten mixed up with his laundry.’”