By Anthony Breznican
August 15, 2014 at 04:00 AM EDT
Atsushi Nishijima

”You know what the truth is? You don’t find Bill Murray,” filmmaker Theodore Melfi says. ”Bill Murray finds you.” This fateful lesson is one learned by many directors, though not all succeed in their quests to recruit the Ghostbusters star for their projects.

Melfi, a longtime commercial director making his feature writing and directing debut on St. Vincent, was certain Murray would be perfect for the title role: a cantankerous old-timer in Brooklyn named Vincent Canatella who drinks too much, smokes too much, gambles too much, and owes too much (to both legitimate businesses, like his bank, and not-so-legitimate ones, like the shady loan shark who’s been threatening him for repayment).

Over the course of Melfi’s bittersweet indie comedy, Vincent unexpectedly softens after bonding with his new next-door neighbors, a single mom, Maggie (Melissa McCarthy), and particularly her 12-year-old son, Oliver (newcomer Jaeden Lieberher). Overwhelmed by her recent divorce, a move, and a new full-time job as a hospital tech, Maggie is just desperate enough to pay the not-exactly-reliable Vincent $11 an hour for Oliver’s after-school care. ”She’s not making good decisions, that’s for sure,” McCarthy says of her character. ”But what else is she supposed to do? She has to work, she has to keep going, she has to take care of her son. That’s what makes her so interesting: What’s she gonna do?”

The linchpin to the film, Melfi knew, was finding the right actor to play Vincent. For a while, Jack Nicholson was interested in the role. When Jack backed out, Melfi went all-in trying to reach Murray, who doesn’t have an agent or a manager. With any luck, though, the notoriously elusive actor would be intrigued by the W.C. Fields go-away-kid-ya-bother-me humor and a heartfelt backstory that could show off his more dramatic acting chops.

Melfi spent months cold-calling the actor’s famous 1-800 number, mailing scripts to random PO boxes via Murray’s lawyer, and even declining one spur-of-the-moment invitation to meet the star in Cannes, France. Then at 8 a.m. one Sunday in 2012, the phone rang at Melfi’s L.A. home. Murray was on the line. ”He goes, ‘Can you meet me at LAX in an hour?”’ Melfi recalls. So the director hurried to the airport and met up with the actor at the United Airlines baggage claim, then rode with him to a golf course near Temecula, Calif., where Murray had a home. During the 100-mile drive, they discussed the screenplay over grilled cheese sandwiches from In-N-Out Burger. ”At the end of it, he goes, ‘Okay, this is great. We should do the movie,”’ Melfi says. ”I say to him, ‘Bill, there’s only one thing.’ ‘What’s that?’ ‘Do you think you could tell someone other than me that this happened?”’

He did, and word of the star’s commitment quickly galvanized the project into existence. McCarthy later jumped aboard, along with Chris O’Dowd as a friendly priest at Oliver’s Catholic elementary school, Terrence Howard as a debt collector, and Naomi Watts as Vincent’s pregnant Russian prostitute/girlfriend.

Once on set, McCarthy had her own offbeat Murray encounter on her first day of shooting. ”I kept thinking, ‘Please don’t freak out. Please don’t say something dumb,”’ says the actress, a lifelong fan of Murray’s. ”Then he stormed into the hair and make-up trailer, made a beeline for me, and was turning me, spinning me. Lifting an arm, putting an arm down. He said, ‘Well, you’re taller than I thought, but you’re still pretty short.’ Literally, he looked me over like a car. It was crazy and I loved it. It made all my nerves go away. That’s a great way to meet Bill Murray.” And she didn’t even have to ride around L.A. with him to do it.