I'm going to give a TL;DR, which will also be relatively long, but significantly shorter than the linked article. I can't remember the order of every detail, but I am posting the facts.
TL;DR: Engineer and former war vet John Kenney moves into a home next door to a pair of "hippies" (as described by their own son) called the Grimes. They carry on a long dispute about their property line. The Grimes' driveway intersected with Kenney's, meaning the couple had to drive onto Kenney's property to park their cars.
Things occurred early on, such as Kenney ratting out Mel Grimes, the husband, building a veranda without permits.
On one occasion, Mr. Kenney, sitting inside his vehicle on his driveway, took a picture of Mrs. Grimes on his property, and the woman reached into the car and snatched the camera, which had a strap, off from Kenney's neck, causing Kenney to slam his door against his car door, injuring Kenney enough to require him to wear a neckbrace.
Both the Grimes and Mr. Kenney took out restraining orders on one another.
Kenney's wife and daughters, who lived in France, as well as his fellow churchgoers all acknowledged that Kenney seemed frightened. He was in his 70's, and he felt fearful of his neighbors assaulting him physically.
Mrs. Grimes went to Kenney's weekly Bible study and berated him in front of his church friends. Mrs. Grimes' own son even states his mother had changed. She used to try to find the good in people, but was now telling her adult son that people can't be trusted.
At some point, Kenney decided to plant a garden on the patch of dirt that these two households were feuding over (aka the strip of land the Grimes drove over to park their cars). The Grimes apparently ran over the garden, and Kenney claimed they killed his garden intentionally.
Kenney went on vacation to France, still wearing his neckbrace, showing signs of his injury. He was diagnosed with PTSD.
The Grimes went to Hawaii.
Both sides returned to their homes in 2007. Kenney consulted a lawyer about the driveway. The lawyer stated Kenney should place a large boulder there. After all, the lawyer said it was Kenney's property.
So Kenney hired a security consultant and had his lawyer present while paying some company to place the boulder. The lawyer and security consultant left after advising Kenney to stay inside his home and call 911 at the first sign of trouble from the Grimes.
Fast forward to a few hours later when the Grimes arrived home. Mr. Grimes, who had a heart condition, ran inside his home, grabbed a shovel and hammer, and started trying to break the boulder. Mrs. Grimes called 911.
Kenney came out to check on the commotion with a loaded pistol. He demanded the Grimes get off his property. Mrs. Grimes, while still on the phone with a 911 dispatcher, began yelling at Mr. Kenney, calling a fat ass.
This is where things aren't 100% certain: Kenney claimed Mrs. Grimes slammed his head against his garage door and Mr. Grimes ran over and hit him with the shovel. The 911 audio recording shows there was a commotion, but it isn't obvious who did what.
One thing is certain, though: Mr. Kenney shot both the Grimes. As they died on the ground, the couples' last words to each other were "I love you."
Mr. Kenney called the police himself, but he never mentioned shooting the couple. He only stated he was assaulted and that he needed the cops there immediately.
He was found guilty for second degree murder of Mr. Grimes and first degree murder of Mrs. Grimes. The jury did not believe Kenney's side of the alteraction (that he was physically attacked by the couple) because, as a juror put it, Mrs. Grimes was on the phone with 911 and wouldn't have attacked Kenney knowing a dispatcher was listening.
Furthermore, Mrs. Grimes was shot in the back. The audio recording also showed that 5 shots were fired, 4 hit the couple (2x each) and a 5th shot, which was heard 15 seconds after the 4th shot, hit the ground.
Kenney was sentenced to life in prison, although he was 72 yrs old at the time, so I don't know if he is even alive today. This shooting happened in 2007.
As of 2013, both the Grimes' and Kenney's homes were vacant. Outside Kenney's house were still buckets of wood he had sorted by size.