Maddula's body was found in the water Thursday night at Wilmette Harbor.
"We want to make sure this investigation is not over," Sushma Maddula, Harsha Maddula's cousin said. "Who was Harsha with last? Who did he speak to last? I still do not know...we need to find the answers."
Officials would not speculate on what led to the drowning. Preliminary autopsy results are expected Friday evening.
Several local law enforcement agencies were involved in the investigation, which included divers searching the lake and police dogs searching the area nearby. His body was found by a fisherman between docked boats.
Maddula was a sophomore at Northwestern University. He came back to campus early to help incoming students. Officials say he was last seen early Saturday morning leaving an office campus party.
"Something happened at this party. We know something happened at this party," Sushma Maddula said. "That's what I want answers to...We really need students to speak up."
"We will look over the interviews and the results of those. That doesn't necessarily mean we will re-interview but we will look at it if it is verifiable and accurate. However, if there is discrepancies in some of the information that is learned, investigators may have to go back and re-interview witnesses that were with Harsha that night," Commander Jay Parrott, Evanston Police Department, said. "We are looking at everything with an open mind. There are obviously medical concerns. Other issues that have come up - alcohol consumption. We're looking at every angle."
Students helped in the weeklong search. Northwestern University President Dr. Morton Schapiro extended his "deepest sympathies" to Maddula's family. He said, "The loss of one member of the Northwestern community deeply affects us all."
"We are profoundly saddened by the loss of Harsha, a cherished member of our Northwestern community," Bradley Stewart, Northwestern student government, said.
On Friday night, hundreds of students and family members gathered in memory of Maddula.
"It's a great act of solidarity that has brought a campus together that's honestly just been confused," said Harsh Shah, student.
"I prayed for him all week. I will continue to pray for him. May his memory be a blessing," said President Shapiro.