The dad of the accused "A-Train Ripper" once bailed his son out of jail even after the lousy kid allegedly beat him and threatened to kill him with a knife — and now kin say they wish the suspect had been left behind bars.

"It would have been better for all of us, and for him, too, to keep him in jail,’’ Oscar Lopez said of his alleged murderous brother, Rigoberto Lopez, to The New York Post on Monday.

Rigoberto, 21, has confessed to stabbing two people to death and wounding two others in a random rampage aboard A trains in New York City over the weekend, police say.

The homeless man had been busted at least four previous times, including for whacking his dad in the left knee with a stick in September 2019, according to authorities and his family.

"My dad didn’t want to give him $20 to eat. [Dad] said, ‘I can give you food, but I don’t want to give you money, because I know what you want to use the money for,’ " recalled Oscar, who lives in The Bronx.

"I don’t know what he was smoking, but I know it wasn’t weed,’’ the sibling said of Rigoberto. "He was addicted to that s- -t, and that’s what he wanted the money for."

Rigoberto was busted for striking his father "with a wooden stick in the back of his left knee causing redness, swelling and bruising to the inside of his left knee and pain,’’ according to a criminal complaint.

The bad seed was charged with misdemeanor assault and aggravated harassment, and while prosecutors asked for $500 bail, the judge freed the defendant on his own recognizance.

A week later, Rigoberto tried to hit up his father again for money — threatening, "I’m going to kill you with a knife’’ if the dough wasn’t handed over, according to court papers and law enforcement sources.

The son was charged with a misdemeanor criminal contempt rap. Prosecutors sought $2,000 bail — but Rigoberto was again ROR’d.

The violent man finally landed behind bars when he went to his dad’s Manhattan workplace the next month, violating an order of protection — and wielded a wooden stick, cutting a cop’s eye, upper lip and hand while resisting arrest, court papers and sources said.

Rigoberto was charged with felony assault on a police officer. Prosecutors sought $10,000 cash bail or $30,000 bond. The judge, however, set cash bail at $5,000 and bond at $7,000 for the suspect.

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"My dad was crying when [Rigoberto] was in jail. We were all crying, we all wanted him out,’’ Oscar said.

"I said, ‘Let me talk to the lawyer and see if we can get him out.’ I got the lawyer on the phone … and he told me what we had to pay to get him out.

"I told my dad, and my dad said, ‘OK, let’s do it.’ We went to court and paid the bond and got him out the same day."

Rigoberto was busted again a little less than a year later for felony drug possession — after cops responded to a call of an emotionally disturbed person in Washington Heights, Manhattan, and found him with 48 glassine baggies of cocaine, according to court records and sources.

He was charged with felony drug possession in the fifth degree and put under supervised release, as prosecutors had requested.

A spokesman for the state Office of Court Administration, Lucian Chalfen, told The Post on Tuesday that there is no way the judges who freed Lopez in previous cases could have foreseen what he is now accused of. 

"Monday-morning quarterbacking the judiciary misses the point," Chalfen wrote in an e-mail. "Adding up this defendant’s prior arrests doesn’t give a Judge insight, even if [jurists] legally were allowed to consider it, into what transpired on the A train.

"Criminal Court Judges are only allowed to make decisions at arraignment, regarding a defendant’s bail and confinement, on the case immediately before them. The legislature provides the guide rails which the judiciary follows." 

Oscar Lopez said his brother lived at home after being freed following his previous latest bout with the law — but was incredibly ungrateful, griping about the abode and bullying everyone around him.

"When he came out of jail, he told us that we didn’t help him. I said, ‘Listen up. I did everything to help you,’ " Oscar said.

"‘I bought you food, I bought you clothes. You want to get into the street life, that’s what you’re going to get. I’ve got my own things to do. … You’re not a baby anymore,’ " he said he told Rigoberto.

"One day, [Rigoberto] said to us, ‘I hate all of you with all my heart,’ " Oscar said.

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"I told my dad, ‘You were crying because he was in jail, now you want him back in jail. What was the point in taking him out and spending all this money for no reason?’"

Oscar said his sibling "was always complaining about how the house was being run.

"He wanted the house how he wanted. And I told him, ‘Listen, you don’t pay no rent, you don’t pay no bills here. So don’t do anything. Just stay in your room. You don’t have the right to do anything here, to change anything.’

"He was always getting in fights with my older brother, but he was all talk, talk, talk,’’ Oscar said.

"He once broke one of my phones. He threw it at the window and broke the window and the phone," he said of Rigoberto.

"He was trying to fight me, and I said, ‘I’m here, what are you going to do?’ And he didn’t do anything. I told him, ‘I’m going to call the police,’ and he left because he was scared.

"Two days later, he came back to get his clothes. He called me at 2 o’clock in the morning.

"We came into my room, and he told me, ‘You see these clothes? You got to put them the other way.’ I said, ‘Listen, these are my clothes, I put them on the way I want, not the way you want. This is not your house anymore.’

"He was talking, talking, talking. I said, ‘Listen up, I’m going to call the police.’ He said, ‘Call the police, I don’t care.’"

Then "he said, ‘Do you want me to kill you?’ I said, ‘I’m going to give you a knife.’ I put the knife in his hand and said, ‘Do what you got to do.’

"He said, ‘No, you’re my brother, I’m not going to do that, you help me a lot,’ " Oscar said. "I said, ‘So why are you talking like that, that you’re going to kill me?’ "

The suspect, who has been hospitalized at least twice for mental issues, remained at the home during the outbreak of COVID-19 in spring 2020 — and had a social worker, but she couldn’t visit because of the virus, Oscar said.

"I spoke to his social worker,’’ the brother said. "She said that the only help he was going to get was by phone. I said, ‘This is not going to help. He’s got big issues. He’s frustrated.’ "

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Rigoberto left the house by May or June, ending up on the streets, then a Brooklyn homeless shelter, where he was living at the time of the weekend stab spree.

He was arraigned on charges including first-degree murder Monday and held without bail.