Just as Lee Harvey Oswald was aiming his rifle at JFK above Dealey Plaza in Dallas, another suspected assassin lurked nearby.

The Cuban expat, Gilberto Policarpo Lopez, was handsome with angular features, a pale complexion and a preference for white V-necks and classic Foster Grant shades. Though he and Oswald appeared nothing alike, they had a lot in common.

Both sought favor from the Castro regime. Both recently had applied for Cuban visas and were denied. Both had fought with their wives and were living alone.

And on Nov. 22, 1963, Lopez was in Texas, though where exactly nobody knows.

What is known is that, on the same day Oswald fired his infamous three shots, killing Kennedy, the 23-year-old homesick drifter crossed from Texas into Mexico then quickly disappeared to Cuba afterward. That fact, coupled with Lopez also having been in Tampa four days earlier, at the same time as JFK, implicates him in the plot, many believe.

“The obvious significance was that Lopez might be fleeing,” writes James H. Johnston in his new book “Murder, Inc.: The CIA Under John F. Kennedy” (Potomac Books), out now, pointing to “his strange travel from Tampa to Texas to Mexico to Havana.”

Born in Cuba, Lopez left in 1960 to avoid being drafted into the military and eventually became a US citizen. But by 1963, he was desperate to return to his homeland.

In the week leading up to Kennedy’s death, Lopez shadowed the president, jetting to Tampa on Nov. 18 for the first leg of the presidential tour. There, he waited for an important call from Cuba, giving him the “go-ahead order” to leave the US and go back to the island nation, a source in Tampa told investigators.

But the call never came, and Lopez departed that night or the next day for Texas. Just days later JFK flew to the Lone Star State and eventually met his death in an open-air motorcade.

No one knows what Lopez did in Texas, but at midnight on the same day JFK was killed, he showed up at the Mexican border in Nuevo Laredo then made his way to Mexico City, presumably by bus. (Just one month earlier, on Oct. 8, Oswald had also traveled to the Mexican capital, where he visited the Cuban consulate and Soviet embassy in a bid to get a visa.)

Mexican border agents viewed Lopez as “suspicious” and snapped the only known photo of him — wearing sunglasses at night.

The CIA station chief in Mexico City “and Mexican authorities were aware of the recent allegation that Lopez had been involved in the assassination, and the allegation was unresolved,” Johnston writes.

At this point, the CIA flagged Lopez as a possible suspect in the assassination plot, writes Johnston, a lawyer on a 1970s Senate committee investigating links between CIA hits and Kennedy’s death.

In Mexico City, where Lopez apparently obtained a “Cuban courtesy” visa, he must have finally got the call he’d been hoping for. On Nov. 27, he hopped on a Cubana Airlines flight to Havana. The flight had waited for hours for Lopez to arrive, then hastily took off after he climbed aboard, though the Mexicans had tried to stall the plane and failed, according to intelligence reports. Lopez was the only passenger.

The CIA assigned the cryptonym it used for the assassination probe, “GPFLOOR” to Lopez, but nothing much else was done, Johnston writes.

After Lopez vanished, the CIA sent its files on him to the FBI, though the bureau didn’t follow up and failed to mention his name to the Warren Commission, which concluded Oswald acted alone. A Senate committee later looked into the allegations but couldn’t prove a thing.

“If the commission had known about Gilberto Lopez’s waiting for a phone call from Cuba about his visa, it might have asked for records of all phone calls from Cuba since Oswald too was waiting to hear about his visa,” Johnston writes. “Not seeking this information is an inexplicable lapse.”

Authorities never pursued Lopez, despite a common belief that Castro almost certainly knew Kennedy wanted him dead, so he acted first, possibly using Lopez’s help.

Lyndon Johnson believed that Kennedy had run a “damned Murder, Inc. in the Caribbean,” giving the Cuban strongman reason to retaliate, according to an Atlantic article by his former speechwriter six months after LBJ died. The CIA had allegedly recruited Chicago mobster Johnny Roselli as well as Rolando Cubela, a Castro rival from Cuba, to kill the dictator.

And yet, even today, many questions go unanswered.

“The confusion that abounded from the top to the bottom of the US government still doesn’t explain why significant leads were never pursued,” Johnston concludes.