ALLEGAN, MI -- Police found the words "My Bad" written in apparent blood on a wall near the body of a 21-year-old woman who was killed and allegedly raped in June at a Wayland area home.

Her cousin, 15-year-old Joshua Lee Keyzer, is accused of open murder in the June 25 stabbing death of Kassandra Keyzer. The teen also stabbed and injured his grandmother.

Court documents detailed the disturbing scene confronting state police troopers when they arrived at the home after Joshua Keyzer's badly injured grandmother called 911.

They found Kassandra Keyzer on an ottoman in the basement, with her arms outstretched. Troopers reported that pants along her left leg, as well as her underwear, appeared to have been cut off.

Police said her body was covered in blood and her hair was saturated with it.

Related: Allegan County teen raped cousin, 21, and killed her, court records say

Kassandra Keyzer's' wounds involved a "deep laceration starting from her chin to the middle of her right cheek" and a stab wound to the front of her neck.

"The words 'My Bad' were written in apparent blood on the north wall above the counter," troopers wrote.

They found a pair of shorts on the floor, with a knife in one pocket, a power cord and lip balm.

Court records indicate Joshuia Keyzer was living part-time at his grandmother's home, in the 3000 block of 10th Avenue.

When police responded June 25, they found Joshua Keyzer standing on the home's roof, covered in blood and holding a knife.

He fell from the roof and into bushes, then tried to run. But troopers used a taser on him and he was quickly subdued.

Joshua Keyzer, who turns 16 in March, was found competent to stand trial in early October. However, another psychiatric exam to determine "criminal responsibility" is now underway.

The court documents describing the crime scene are part of a state police lab report that incorporates troopers' statements.

Police allege the teen also cut his grandmother's throat during the attack at the 10th Street home.

The grandmother, 67-year-old Sharon Keyzer, recovered from the knife assault but died in late December from cancer.

In her obituary, relatives said she died Dec. 28 after a "very courageous battle with cancer."

Allegan County Chief Assistant Prosecutor Rob Kengis said prosecutors were aware that the grand mother had cancer and do not believe the knife attack contributed to her death.

According to the court documents, the letters in blood in the basement were not the only ones located in the house.

Police also found an "S" written in apparent blood on the wall of a master bathroom, off the master bedroom where emergency crews treated Sharon Keyzer for her injury.

No trial date is set in the case.

E-mail John Tunison: jtunison@mlive.com and follow him on Twitter at twitter.com/johntunison