Frederick Ramsay, the former Alexandria businessman accused of hiring three men to kill his business partner, was acquitted of capital murder yesterday, ending a three-year police investigation into the slaying.

Ramsay burst into tears when the verdict was announced and then, with his steel-blue eyes bleary and his hand over his heart, walked over to jury box in Alexandria Circuit Court and said: "Thank you for believing me. I am innocent."

Ramsay, 41, former president of Suburban Electric Co. in Alexandria, was charged with first-degree murder and accused of hiring three men to kill his partner, William B. Young, 54, to collect on a $150,000 life insurance policy.

Young, vice president of the now- defunct electrical contracting firm, was killed when a bullet from a .22-caliber rifle ripped through his chest on Nov. 27, 1981.

During the six hours the jury deliberated Thursday and yesterday, Ramsay's family and attorneys paced outside the fourth-floor courtroom, often weighing aloud the evidence presented since the trial began Monday.

Defense attorneys A. Albert Ahern and Louis Koutoulakos told Ramsay's mother, sister and brother that they believed Ramsay would be acquitted because the only government witnesses who testified that Ramsay ordered Young's murder were convicted felons.

One of the 12 jurors, who asked not to be named, said she found Ramsay not guilty "because there was a lot of circumstantial evidence against him, but it was tough to believe what Threatt said."

Ralph Threatt, 44, the government's prime witness, told the jury that Ramsay wanted Young "liquidated, eliminated."

Threatt said he paid Thomas Ebron, 26, and Charles Joseph, 36, $10,000 to kill Young. Both Ebron and Joseph testified that they met Threatt in their neighborhood park four years ago and accepted his murder-for-hire offer.

Ebron and Joseph, who have pleaded guilty to first-degree murder, told the jury they were heroin addicts. But only one, Ebron, testified that he met Ramsay and discussed the murder plot with him.

In exchange for Threatt's cooperation -- which led to the arrests of Ebron and Joseph, and his testimony against Ramsay -- the commonwealth's attorney's office granted Threatt immunity from prosecution. Ebron, who wielded the gun, could be sentenced to life imprisonment and Joseph to 46 years.

"It was clear that without making some agreement with him Threatt , we could not have located Ebron and Joseph and put this case on," said Deputy Commonwealth's Attorney S. Randolph Sengel.

"It was a difficult case," Sengel said, "but I think homicide detectives Bill Scott and Tom Moorehead did a great job."

Scott and Moorehead began investigating Ramsay more than three years ago, when they discovered that Suburban Electric had taken out a $150,000 company life insurance policy on Young and that a clause added later provided double indemnity in case of accidental or sudden death.

The prosecution alleged that Ramsay, who was having financial troubles with his now-defunct firm, instructed Threatt to hire Ebron and Joseph to kill his partner so that he could get the $300,000.

Within 24 hours of the murder, an insurance agent testified, he was contacted by Ramsay's brother, Tracy, about the claim. During the trial, three of Young's relatives testified that Ramsay told them the company had no insurance on Young.