Individuals who were not involved in protests against last weekend's inauguration of Mexican President Enrique Peña Nieto were arrested during the disturbances, the ombud's office in this capital said.
People with "nothing to do with the protests," which spilled over into clashes with police, looting of stores and destruction of public and private property, were taken into custody, Mexico City Ombud Luis Gonzalez Plascencia told W Radio on Wednesday.
A total of 69 people were booked and jailed in connection with the violence, which left 100 injured, caused considerable material damage and prompted an investigation by the Mexico City ombud's office, known as the CDHDF.
Gonzalez said his office has received a "significant number" of reports indicating that individuals who were simply walking in the area, in some instances far from the protests, were arrested.
Several people also have filed reports concerning arrests by plainclothes police during the violent protests.
The disturbances erupted in different parts of the Mexican capital including its historic center and Juarez Ave., where the municipal police force intervened.
Asked if some plainclothes cops infiltrated the demonstrations and provoked clashes with uniformed police, the ombudsman said he had not received reports to that effect.
The CDHDF's preliminary report, due to be released Thursday, is expected to denounce arbitrary arrests during the most serious violent incidents in recent years in the Mexican capital.
The report will be based on accounts provided by attorneys and family members of detainees, as well as videos uploaded in recent days on social-networking sites.
Peña Nieto, the candidate of the Institutional Revolutionary Party, or PRI, won the July 1 presidential election with 38.21 percent of the vote, while leftist candidate Andres Manuel Lopez Obrador took second place with 31.59 percent, according to the final official tally.
Lopez Obrador and his supporters claimed the result was marred by widespread fraud, but Mexico's top electoral court upheld the victory in August.
The judges found that insufficient evidence was submitted of biased and unequal news coverage in favor of Peña Nieto, particularly by No. 1 TV broadcaster Televisa, even though Britain's Guardian newspaper published e-mails about a secret unit at the network whose mission was to promote the PRI hopeful.
They also dismissed evidence of deliberate distortion in pre-election polls, use of illegal funding and excessive campaign spending, vote buying and coercion, improper intervention in the election by state governors and other public officials and irregularities on election day.
The conservative National Action Party, or PAN, which governed Mexico from 2000 until Saturday, also joined with Lopez Obrador in demanding an investigation of the PRI's finances.
But National Action, whose candidate, Josefina Vazquez Mota, finished a distant third in the presidential election, did not formally contest the election results.
The non-partisan Yo soy 132 student movement also has held a series of protests and other events this year to block the "imposition" of Peña Nieto as president.
The PRI, which governed Mexico from 1929 to 2000, lost the 2000 presidential election to the PAN and finished third in 2006.
During that 71-year reign, the PRI relied mainly on patronage and control of organized labor and the mass media, though it was not above resorting to outright vote-rigging and even violence. EFE