The pair were originally charged with first-degree murder, aggravated assault, and related crimes.
Court records revealed that Arunkumar Ingle had planned to get a counterfeit passport, fake his own death, and move to India with a woman he met over the Internet.
Parth Ingle told the court Thursday that on the day of the killing, he confronted his father about his plans.
He testified that his father threatened to kill him, his mother, and his sister, and began to choke him.
"I was terrified," the son testified.
His father struck him with a baseball bat, he testified, before he was able to wrestle it away.
"I lost control of myself," Parth Ingle said, admitting that he beat his father to death with the bat. His mother was present during the killing.
While police believed from the start that Arunkumar Ingle knew his killer, it would be three years before charges were brought against Parth Ingle and his mother, who initially claimed ignorance as to who committed the crime.
To help solve the case, investigators arrested Parth and his sister Avnee, 28, on charges of wiretapping and intercepting e-mails after finding evidence they had found ways to compromise their father's computer in an effort to establish he was having an affair.
The e-mails revealed that since 2003, Arunkumar Ingle had been having an affair with a Philadelphia woman. The woman later testified that Ingle was planning on getting a false passport, faking his own death, and moving with her to India.
In December 2011, Parth Ingle was found guilty of putting spyware on his father's computer to capture passwords to e-mail accounts and was sentenced last December to two years' probation.
Avnee Ingle was acquitted.
Within weeks, Parth Ingle and his mother were arrested for murder.
Contact Mari A. Schaefer at 610-892-9149, firstname.lastname@example.org or @MariSchaefer on Twitter.