Reyes had been bound by the hands and feet and stuffed inside the suitcase. The official cause of her death has not yet been revealed.
Amateur sleuths pointed the finger at Reyes' ex-boyfriend. The pair broke up a week before she was murdered. One wrote on Twitter: "He's looking so f***ing (suspicious)".
But police in Greenwich arrested another of her ex-boyfriends, Javier Da Silva, on Monday afternoon.
Her most recent ex wrote on Twitter: "It wasn't me. It was the guy before me."
Detectives from her hometown, accompanied by detectives from the town where she was found, arrested a "suspect in New York who had fraudulently used the ATM card of victim Valerie Reyes", they said in an official statement.
"The arrested individual is also believed to be involved in the death of Valerie."
Da Silva, 24, is a resident of Queens, New York. He holds dual citizenship with Venezuela, and it is believed he broke up with Reyes a year ago.
Connecticut-based news journalist John Craven reported Da Silva admitted to his role in Reyes' death, telling investigators the pair had sex before "she fell to the floor and hit her head".
Da Silva reportedly told investigators he taped her mouth and put her inside the suitcase where a road worker later found her body.
Valerie's mother Norma last week told reporters she could not move past the conversation she had with her daughter the night before she went missing.
Her most pressing question was: "Who made her feel (scared)?"
"I asked about her ex-boyfriend. And she said, 'No'," Norma said, referring to her daughter's former partner who it's believed she separated from on January 24.
"We don't even understand," Norma said. "The only thing that's weird is she was frightened for her life, and then somebody ends up taking her life."
Reyes was fully clothed when she was found. An autopsy was carried out on Wednesday night, but the cause of death has not been disclosed by the coroner.
Police believe she was killed elsewhere and dumped in Greenwich, 24km from her home in New Rochelle.
Several items were missing from Reyes' apartment, police said. Those items included an iPhone, an iPad, her wallet, several items of clothing and bedsheets.
Reyes' family hired a private investigator the day after she went missing, according to the Westchester Journal.
The newspaper reports she was spotted by CCTV cameras at an ATM in Manhattan at 2am last Wednesday. Her bank card was also used later that morning at another ATM, but there was no surveillance footage of the second withdrawal.
A candlelight vigil was organised on behalf of the Reyes family on Thursday night. Hundreds of people gathered at Glen Island Park, a 60-hectare island connected to New Rochelle.
Reyes' father issued a statement after her body was found.
"At this unimaginably difficult time, we are asking for love, support and respect to our family for the loss of my beautiful daughter Valerie Reyes who is now resting in heaven," he said.
Greenwich Police Captain Robert Berry issued a statement last week relaying the community's "heartfelt condolences".
In the days after the Barnes & Noble employee went missing, friends and family members shared her picture on social media and pleaded for locals to keep an eye out for her or get in touch if they spotted her.
Among them was a man who identified himself as Valerie's boyfriend. On January 30, he wrote the following message on Twitter: "My girlfriend Valerie is now officially reported as a missing person nationwide by the authorities. Please contact me if there is ANY kind of information."
He later tweeted the broken heart emoji and told those who offered support he was "finding it difficult to come to terms with everything going on".
Today he tweeted: "#JusticeforValerie" and "What's done in the dark will always find a way to shine".
