Forensic evidence
There was not much evidence at the murders, but BTK sent in lots of evidence. There was semen found at a few of the crime scenes and ligatures. The police knew he drove a black jeep from surveillance video from a parking lot. They also had evidence that he couldn't write very well and wasn't very literate. He messed up in the letters he wrote. The floppy disk he sent to the police was the key piece of evidence that caught him. It had his name on the floppy disk along with things dealing with the church.
Forensic techniques
DNA analysis:
Dennis Rader's daughter offered up a DNA swab when she suspected her father had something to do with it. The DNA was a close match the semen found at the crime scenes. They had to call in a forensic serologist to collect the DNA and to process it and match it.
Handwriting:
The police brought in a handwriting specialist to look at the letters BTK sent in and matched them to the original one. They helped identify the suspect that was suspected of the BTK but wasn't.
Technology:
The police had to use the forensic technology specialist to hack into the floppy disk that Rader sent into the police. When they hacked it they found the name "Dennis" and some church documents. This was the crucial part of the evidence that eventually locked up BTK.
Dennis Rader's daughter offered up a DNA swab when she suspected her father had something to do with it. The DNA was a close match the semen found at the crime scenes. They had to call in a forensic serologist to collect the DNA and to process it and match it.
Handwriting:
The police brought in a handwriting specialist to look at the letters BTK sent in and matched them to the original one. They helped identify the suspect that was suspected of the BTK but wasn't.
Technology:
The police had to use the forensic technology specialist to hack into the floppy disk that Rader sent into the police. When they hacked it they found the name "Dennis" and some church documents. This was the crucial part of the evidence that eventually locked up BTK.