The case has all the twists and turns of a crime novel.

The victim, Arunkumar Ingle, a 55-year-old Boeing Co. engineer from Middletown Township, Delaware County, had planned to fake his own death and run off to India with his Russian mistress, using a fake passport. He would leave behind $3.6 million in life insurance to take care of his family.

Now, nearly four years after he was stabbed and beaten in his bedroom - his testicles severely bruised - investigators say anger and financial gain were the motives for his 25-year-old son, Parth, to kill him.

On Wednesday, police charged Parth Ingle with homicide, aggravated assault, terroristic threats, and related crimes including conspiracy, a charge investigators would not comment on, in his father's death.

"Relentless work" by troopers and the Delaware County District Attorney's Office led to the charges, said Anthony Sivo, state police commander at Troop K in Media. He would not comment beyond the 25-page affidavit.

Defensive wounds indicate Arunkumar Ingle fought for his life.

There were no bloody footprints or blood trail, no discarded clothing or murder weapon. There was no evidence of a break-in; nothing was ransacked or missing. There were no calls for assistance. Neighbors did not remember hearing loud noises or seeing any suspicious activity.

Investigators said at the time that Arunkumar Ingle knew his killer.

"There is nothing here they didn't know six months after the homicide," said John E. Kusturiss, Parth Ingle's defense lawyer. His client is being held in the Delaware County prison without bail.

This is not the first time Parth Ingle has faced charges in the case.

Two weeks ago, he was sentenced to two years' probation after being found guilty of unlawfully using a computer when he installed eBlaster software to obtain his father's e-mails. His older sister, Avnee, was also charged but was acquitted. Jurors were told only that Arunkumar Ingle had died.

Testimony and the affidavit offer this narrative:

On Jan. 21, 2008, Bhavnaben Ingle, Arunkumar Ingle's wife, told police she had spent the night at her son's home in Pottstown after her husband told her he was having a meeting and did not want her in the house.

Parth Ingle had picked up his mother. On the way to Pottstown, he asked her to teach Devika Brahmbhatt, then his girlfriend and now his wife, some Indian recipes. Later, the three went to a store.

Bhavnaben Ingle returned home the next day with Avnee Ingle to drop off groceries before heading to work at the family's 7-Eleven store in Newark, Del. She then discovered her husband's body.

In 2003, Bhavnaben Ingle had suspected that her husband was having an affair and gave her son permission to install the spyware on the computer to capture her husband's passwords.

Parth Ingle then learned that his father was having an affair with a Philadelphia woman, Anna Sudakevich.

Sudakevich has said she did not know that Ingle was married until fall 2007, when Parth Ingle showed up at her Northeast Philadelphia door to confront his father. He had secretly attached a GPS device to his father's car.

Authorities cited inconsistencies in the family's stories about the slaying of Arunkumar Ingle.

Parth Ingle told police that he had picked up his mother between 8 and 8:15 p.m. Jan. 20 and that they had gone to his Pottstown home.

Records show calls were made from his phone between 8:43 and 10:02 p.m. from a Pottstown location. At 11:38 p.m., a call from his phone was made in the area of the family's Middletown home.

Parth Ingle told police that he was shopping that night in a Pottstown-area store with his mother and girlfriend and that they left the store at 1:43 a.m. He said they spent the rest of the night watching HGTV and doing laundry before going to bed after 3.

A text from Devika Brahmbhatt's cellphone was sent at 2:14 a.m. to Parth Ingle's phone: "hey hun waits groin on everything OK."

The day she discovered her husband's body, Bhavnaben Ingle told police: "If I knew who did it, what would happen to this person?" She told investigators that after the funeral, she was going to ask Parth Ingle whether he had committed the crime. She then ended the interview.

In 2008, Parth Ingle was self-employed and lived off money his mother gave him, according to court records.

He had a $29,000 loan on a Nissan Maxima, $8,000 on a Suzuki motorcycle, credit-card debt of $5,900, and a mortgage of $220,000. Documents show that he was two payments past due on the Nissan and that the Suzuki was in "repossession status." His wife had a $41,000 second mortgage and $12,000 in credit-card debt.

"Are they trying to make a big deal about them being in a little bit of debt?" Kusturiss asked. Most Americans carry home, car, and credit-card debt, he said.

Three days after the killing, police served a search warrant at Parth Ingle's house and found traces of DNA in a sink trap. Tests could not "exclude" the victim as a contributor to the mixture.

There was also a list with Parth Ingle's fingerprints on it. It read: "Statue. Life insurance. What would happen to you guys. Can I be arrested another country."

Contact staff writer Mari A. Schaefer at 610-892-9149, mschaefer@phillynews.com, or @MariSchaefer on Twitter.