Criminologist Dr Paul O'Mahony strongly criticised the Garda Síochána at yesterday's sitting of the Joint Oireachtas Committee on Justice, Equality, Defence and Women's Rights.
He told the committee there were "systematic problems" in the way the Garda Síochána managed evidence, interrogations and the detention of suspects.
"There is a problem in our policing culture that has not been properly addressed and this should warn us against tampering with the balance of present safeguards to make convictions easier to obtain," he said.
Dr O'Mahony is a former Department of Justice psychologist and has written a number of books on criminal justice.
He highlighted the Dean Lyons case, where the now-deceased heroin addict was wrongly charged with the murder of two women in Grangegorman. It showed how easy it was for police to extract false admissions from certain susceptible witnesses, Dr O'Mahony said.
Referring to various "scandals" that involved gardaí, Dr O'Mahony said the force was not taking the kind of remedial action one would expect. "Serious effort is not being put into human rights and civil liberties training within the training college. There are no monitoring systems," he said.
"There is a kind of deference to the Garda Síochána which has allowed it to escape taking the right kind of action and putting its own house in order."
On the intimidation of witnesses, he said local people had "lost faith in the capacity of the law to protect them".
"Given that this is the case, the State should be slow to charge a threatened person with perjury or making false statements under oath when it is unable to guarantee that person's freedom and security." He said there was a "great deal" of intimidation in more deprived areas "especially areas riddled with drug abuse. Most of this intimidation is related to low-level criminal activity and vandalism and even includes intimidation by teenagers and pre-teens."
This greatly impacted on the quality of life of many vulnerable older people. He said the most hopeful strategy was a preventative one, building cohesion and solidarity in communities.
Dr O'Mahony said that while people had heard about many poorly organised criminal gangs, the State had a problem with highly organised international gangs involved in drugs, prostitution, people-trafficking, fraud, counterfeiting and protection. "These gangs are not as obvious and are more successful at evading the attention of police."
He also said juries did not represent society as "the middle classes and professional people almost entirely evade jury duty".
"Students, retired people and housewives are the type of people who turn up and are selected for jury service. The professions such as teachers, doctors and so on are very easily excused from jury duty."
Asked about the criticism, a Garda press office spokesman said he was not aware of the remarks and could not comment until they were studied in full.
