It wasn't immediately clear if prosecutors meant to retry Menendez, who faces more than a dozen charges in connection with an alleged bribery scheme with a wealthy friend.
The most serious of the charges carries a maximum penalty of 20 years in prison.
The trial is in its 11th week. I think we have a real hung jury, " said Lowell.
The jury's note declared that although they had reviewed the evidence "slowly and thoroughly and in great detail", the panel's split remained irrevocable.
Should the jurors fail to reach a verdict, the judge will declare a mistrial, which would be a temporary victory for the embattled Democrat.
Walls could have instructed the jury it is allowed to reach a verdict on some counts but not others, though that type of instruction typically would have followed a note from the jury inquiring about that option.
If they don't reach a verdict Thursday, deliberations might resume Monday.
The defense sought a mistrial after four jurors and three alternates told the judge they heard media reports over the weekend about Arroyo's comments. A day later she changed her mind about the count 18 conviction. Menendez and Melgen are charged with running a bribery scheme between 2006 and 2013 in which Menendez lobbied government officials on Melgen's behalf in exchange for luxury vacations and flights on Melgen's private plane.
It is possible for Menendez to face trial again, but for now, it seems he is off the hook. At the end of the more than 10-week.
The bribery trial of New Jersey Sen. Both were found guilty by juries to later have those convictions overturned because of a U.S. Supreme Court ruling that raised the bar on what is considered public corruption.
Menendez said earlier this month he was convinced he'd be exonerated.
Jurors also failed to reach the unanimous conclusion that Menendez had "knowingly and willfully" falsified his annual disclosure forms in an attempt to hide the gifts from Melgen, an allegation in the last count of the indictment against the men.
Prosecutors are trying to convince Walls that deliberations should continue. Melgen faced the same charges except for the false statements accusation. Bob Menendez and a wealthy friend. Neither took the witness stand during the 11-week trial, which included more than 55 witnesses, from Federal Bureau of Investigation agents to plane pilots.
In return, prosecutors said, Menendez pressured government officials on Melgen's behalf over an $8.9 million Medicare billing dispute and a stalled contract to provide port screening equipment in the Dominican Republic, and also helped obtain USA visas for the 63-year-old doctor's girlfriends.
The senator also helped foreign women get US visas to visit the married doctor in Florida.
According to prosecutors, Melgen essentially put Menendez on the payroll and made the politician his "personal senator", available as needed.
Defense lawyers said there was no corrupt motive behind the friends exchanging gifts and vacationing together. On November 13, the jurors sent Judge Walls a note telling him they were deadlocked on a decision.