Police Superintendent Garry McCarthy said at a Monday press conference that Mr Watkins had earlier robbed Willis, prompting the spray of bullets.
The man turned himself in on the weekend though he is yet to provide a statement and no weapon has been recovered, McCarthy said.
'I don't want to use cliche terms, but police were pounding the pavement,' McCarthy said, according to DNA Info.
'We don't have one individual who's stepping up to help us,' McCarthy said in late March, though it appears the community came forward with information and photos in the intervening months. Police initially said Mr Watkins had links to the Gangster Disciples clique though his family denies he has ties to gangs.
Little Jonylah was struck by a bullet on March 11 while she sat in a minivan with her father who was also shot three times but survived.
Koman Willis is facing first degree murder and aggravated battery with a firearm charges after he allegedly shot dead baby Jonylah Watkins while aiming for her father, Jonathan Watkins.
Reverend Corey Brooks, who held a emotionally-charged funeral service for the baby in March and is acting as a spokesman for the family, said Jonylah's parents had been cooperating with police to find their daughter's killer.
Brooks added that Watkins, 29, who has a lengthy criminal history and was criticized by the community in the wake of his daughter's death, hadn't been asked by police to identify a possible shooter.
Reverend Brooks' church New Beginnings Church of Chicago was offering a $5,000 reward for information that leads to an arrest.It's unclear if such a tip led to the arrest. The family have called on the 'cowardly' gunman to turn himself in, which is what police say happened on the weekend.
Jonylah had been sitting in her father's lap in the driver's seat of a parked minivan when a Willis allegedly opened fire.
The baby, whose mother was working at McDonalds at the time, died the next morning from her wounds after surgeons spent hours trying to save her.
McCarthy initially said the shooting appeared to be gang-related, though detectives didn't have a specific motive until Monday.
Despite the shocking crime, neighbors were refusing to cooperate with police.
In March, Mr Watkins told the Chicago Sun-Times from his hospital room that he was devastated by the death of his infant daughter.
'I was trying to help. I was trying to help. I was trying to help her,' he said, breaking down.
Still, he claims he has no idea who shot at them or why he was targeted.
Willis allegedly shot at the father and baby from an alley and hit Mr Watkins in the cheek and buttocks, Chicago police spokesman John Mirabelli said.
The gunman then got into a nearby blue minivan and fled the scene, according to DNAinfo.
When I read this story I was very much sadden by the lack of love we have for one-another. Their are times we read stories like this and have no words but just say, Why?
Well scripture is clear and Yah holds nothing back from His wicked children in this captivity. The Most High is dealing with His people and their wickedness; so much so in these last days that even your sweet innocent baby will not escape His judgment. Yah says, "I will also forget thy children." This is a hard pill to swallow but is very obvious when you see the countless innocent babies and young children that are lost daily among Israel, at the hands of our enemies and fellow Israelites alike.
We must return to the law of Yah to restore our people. Our people have become dull of hearing and understanding Yah's laws and perish because of it. Jeremiah 5:4 Therefore I said, Surely these are poor; they are foolish: for they know not the way of the Most High, nor the judgment of their Mighty One.
The Most High has forgotten our children because we have forgotten His laws and commandments. We are like ones dried up with thirst not having any knowledge our wisdom from the Most High. Isaiah 5:13 Therefore my people are gone into captivity, because they have no knowledge: and their honorable men are famished, and their multitude dried up with thirst.
I cry out to the Most High and pray for our nation to wake up even though I know 2/3rds of our people will remain wicked and be lost but I cry all the same for the remnant to return to Yah and repent to take away the reproach. Zechariah 13:8 And it shall come to pass, that in all the land, saith Yah, two parts therein shall be cut off and die; but the third shall be left therein.
My cry is for that righteous remnant that will hear and repent. Isaiah 10:21,22 The remnant shall return, even the remnant of Jacob, unto the mighty Yah. For though thy people Israel be as the sand of the sea, yet a remnant of them shall return: the consumption decreed shall overflow with righteousness.
Read more: http://www.dailymail.co.uk/news/article-2331836/Jonylah-Watkins-Chicago-gang-member-charged-murder-shot-dead-month-old-girl-dad-stole-video-game-console.html#ixzz2Uelc93va
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